Gaseous fuels may provide several advantages over liquid fuels for operating an internal combustion engine. For example, gaseous fuels may be inexpensive, may have high octane rating, and may mix more readily with air at colder ambient temperatures. Improved fuel-air mixing may reduce engine emissions and it may also improve engine starting at lower ambient temperatures. However, gaseous fuels may also present challenges for powering internal combustion engines. For example, gaseous fuels may be port injected to an engine, but the engine may exhibit a loss in output power as compared to if the same engine were operated with liquid fuel. On the other hand, if the gaseous fuel is direct injected, it has to be stored at a higher pressure so that it may be injected into a cylinder during the cylinder's compression stroke. A direct injection gaseous fueled engine may provide improved power output, but a significant amount of fuel stored under pressure in a fuel storage vessel may not be usable because pressure in the storage vessel is reduced as fuel is consumed by the engine. Consequently, the vehicle's driving range may be reduced.
The inventor herein has recognized the above-mentioned disadvantages and has developed an engine operating method, comprising: directly injecting a gaseous fuel to an engine in response to a pressure of a gaseous fuel stored in a fuel tank exceeding a threshold pressure; and activating a gaseous fuel pump only when the pressure of gaseous fuel stored in the fuel tank is less than or equal to the threshold level.
By selectively activating a gaseous fuel pump, it may be possible to extend a vehicle's operating range even though gaseous fuel stored in a fuel storage tank is at a lower pressure. In particular, a gaseous fuel pump may be activated when pressure in a gaseous fuel storage tank of vessel does not reliably support direct injection of gaseous fuel into engine cylinders. However, if pressure in the gaseous fuel tank supports direct injection of gaseous fuel into engine cylinders, the gaseous fuel pump may be deactivated and gaseous fuel may be directed from the fuel tank to engine cylinders. In this way, the gaseous fuel pump is operated only when gaseous fuel stored in the fuel tank is less than a pressure that supports direct injection of gaseous fuel into engine cylinders. Additionally, transmission shift schedules and torque converter locking may be adjusted if the gaseous fuel pump has a flow capacity less than is desirable for operating the engine at all speeds and demand torques.
The present description may provide several advantages. For example, the approach may improve a vehicle's driving range. Further, the approach may allow gaseous injection of gaseous fuel through only direct injectors as opposed to systems that utilize both port and direct injection. Further still, the approach may adjust vehicle operation to accommodate a lower flow rate gaseous fuel pump so that system cost may be reduced.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.